1. The Field of the Invention
The present invention relates to a new process for the preparation of primary aromatic, cycloaliphatic, aliphatic or arylaliphatic amines.
2. The prior Art
It is known that the amines may be prepared by degradation of the amides of the corresponding acids, containing one carbon atom more than the amine which it is desired to obtain, by treatment with hypochlorite or hypobromite in alkaline medium (Hofmann degradation); said reaction may be represented by the following overall equation (when sodium hydroxide is used as the alkaline hydroxide and chlorine as the halogen): EQU R--CONH.sub.2 +Cl.sub.2 +4NaOH.fwdarw.R--NH.sub.2 +2NaCl+Na.sub.2 CO.sub.3 +2H.sub.2 O
wherein R represents an organic radical.
This reaction is practically carried out in the industry in two stages which may be represented by the following equations: EQU 2NaOH+Cl.sub.2 .fwdarw.NaCl+NaClO+H.sub.2 O (a) EQU RCONH.sub.2 +NaClO+2NaOH.fwdarw.R-NH.sub.2 +NaCl+Na.sub.2 CO.sub.3 +H.sub.2 O (b)
As it appears from these equations, four mols of sodium hydroxide (or of other alkali hydroxides) are required for each mol of amine obtained. This is because two mols of hydroxide are used up to obtain one mol of hypochlorite, while two more mols are necessary for the Hofmann degradation proper.
The Applicant has now surprisingly found that it is possible to obtain the same result by using a smaller molar ratio of alkali hydroxide employed to amine obtained; this may be achieved by reacting, at a pH less than or equal to 7, the amide (RCONH.sub.2) firstly with gaseous chlorine in the presence or absence of a diluent, and subsequently reacting the formed N-monochloroamide with an alkali and/or an earth-alkali hydroxide, such as barium or calcium hydroxide, to obtain the corresponding amine (RNH.sub.2) with comparable yields. In the case that sodium hydroxide is used as the alkali hydroxide and calcium hydroxide as the earth-alkali hydroxide, the reactions according to the invention may be represented as follows: EQU RCONH.sub.2 +Cl.sub.2 .fwdarw.RCONHCL+HCl (.alpha.) EQU RCONHCL+2NaOH.fwdarw.RNH.sub.2 +NaHCO.sub.3 +NaCl (.beta.) EQU 2RCONHCL+3Ca(OH).sub.2 .fwdarw.2RNH.sub.2 +2CaCO.sub.3 +CaCl.sub.2 +2H.sub.2 O (.gamma.) EQU RCONHCL+NaOH+Ca(OH).sub.2 .fwdarw.RNH.sub.2 +NaCl+CaCO.sub.3 +H.sub.2 O (.delta.)
The economic advantage of using, for each mol of amine formed, only two mols of sodium hydroxide or 11/2 mols of calcium hydroxide, or a mixture of the two, is obvious, both because a smaller quantity of hydroxides is used, and because calcium hydroxide is considerably cheaper than sodium hydroxide.
The object of the present invention is therefore a process for the preparation of amines of the RNH.sub.2 type, wherein R represents a hydrocarbon radical containing up to 18 carbon atoms, in particular an aliphatic, arylaliphatic, cycloaliphatic or aromatic radical, characterized by the fact that an amide having an RCONH.sub.2 formula, wherein R has the aforesaid meaning, is reacted, at a pH less than or equal to 7, firstly with gaseous chlorine, in the presence or in the absence of a diluent, and that the N-chloroamide thus formed is subsequently reacted with an alkali hydroxide and/or an earth-alkali hydroxide in particular barium or calcium hydroxide. Preferably the molar ratio of the (OH).sup.- groups of said hydroxides with respect to the --(CONHCl) group of said amine is practically maintained smaller than or equal to 3:1.
The saving of alkali hydroxide, earth-alkali hydroxide, or the mixture of the two, may practically be as high as 50% with respect to what is required by the classic Hofmann reaction.
The chlorination of the amide RCONH.sub.2 is conveniently effected at a temperature comprised between -20.degree. and +80.degree. C., preferably between +10.degree. and +20.degree. C., optionally under pressure.
As a diluent it is possible to use e.g. water, chloroform, carbon tetrachloride, trieline, and all the diluents which do not undergo chlorination in the sunlight in the presence of elementary chlorine; obviously it is possible to effect the chlorination of the amide also in the presence of a mixture of said diluents.
The reaction between the N-chloroamide obtained and the alkali hydroxide and/or the earth-alkali hydroxide, is effected in the presence of a suitable diluent (e.g. water) at a temperature comprised between 0.degree. and 100.degree. C. and preferably between 0.degree. and 80.degree. C.
As an alkali hydroxide, e.g. potassium or preferably sodium hydroxide may be used. Preferably calcium hydroxide is used as an earth-alkali hydroxide. It may be convenient to employ at least a part of an alkali hydroxide in the hydroxylated component. The amine obtained is separated by conventional methods known in the literature with reference to the specific amine formed.
According to the present invention, it may be preferable to separate the N-chloroamide from the reaction mixture before reacting it with the alkali and/or earth-alkali hydroxide/hydroxides. Obviously it is also possible to employ a mixture of hydroxides of several alkali and/or earth-alkali metals.
According to the present invention it is possible to operate either discontinuously or continuously.
By operating according to the present invention, a further advantage is attained: actually the separation of the two reaction stages, according to the present invention, permits to employ the cheaper calcium hydroxide which, while it is indicated as operative in the known art, is practically hardly usable because of the instability of the calcium hypochlorite.
The amines obtained by the process according to the invention form a further object of the present invention.
The following examples are illustrative but do not limit the present invention.